1. Field of the Invention
The invention relates to a steering control apparatus that outputs an operation signal to a steering system.
2. Description of the Related Art
For example, Japanese Patent No. 4269451 describes a steering control apparatus that outputs an operation signal to a steering system including a variable-steering-angle-ratio actuator. The actuator varies a steering angle ratio that is a ratio between the steering angle and a steered angle while transmitting a torque applied to a steering wheel to steered wheels. The control apparatus executes what is called differential steering processing of setting an operation angle through which a rotation angle for an output side of the variable-steering-angle-ratio actuator is changed with respect to a rotation angle for an input side thereof that is the steering angle such that the operation angle is larger when a variation speed of the steering angle is high than when the variation speed of the steering angle is low.
For the steering system, upper limit values are specified for the steering angle and the steered angle according to the structure of the system. The steering system also includes a steering control apparatus that performs angle limitation control in which increases in steering angle and steered angle are limited before the steering angle and the steered angle reach the structural upper limit values thereof. For the steering control apparatus, the inventor has found that the steering system may be vibrated when the differential steering processing is executed in a region where the angle limitation control is performed. Even if the steering control apparatus is not equipped with a controller that performs the angle limitation control, the steering system may be vibrated when the differential steering processing is executed near the structural upper limit values. Even if the differential steering processing is based on a steered angle velocity of steered wheels rather than on the variation speed of the steering angle, the steering system may also be vibrated when the differential steering processing is executed near the structural upper limit values or in the region where the angle limitation control is performed.